Loans and Allowance for Loan Losses - Aging of Gross Loans, Broken out by Portfolio Segment and Class of Financing Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	$ 4,294	$ 10,563
60 - 89 Days Past Due	1,160	10,063
Greater Than 90 Days Past Due	5,702	2,288
Total Past Due	11,156	22,914
Current	9,903,043	9,001,334
Loans Past Due 90 Days or More Still Accruing Interest	24	19
Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	4,203	6,551
60 - 89 Days Past Due	1,160	387
Greater Than 90 Days Past Due	24	19
Total Past Due	5,387	6,957
Current	8,949,291	8,151,780
Loans Past Due 90 Days or More Still Accruing Interest	24	19
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	0	111
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	0	111
Current	921,473	827,121
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Total gross loans excluding impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	4,203	6,662
60 - 89 Days Past Due	1,160	387
Greater Than 90 Days Past Due	24	19
Total Past Due	5,387	7,068
Current	9,870,764	8,978,901
Loans Past Due 90 Days or More Still Accruing Interest	24	19
Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	91	3,901
60 - 89 Days Past Due	0	9,676
Greater Than 90 Days Past Due	5,678	2,269
Total Past Due	5,769	15,846
Current	32,279	22,433
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Software
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	1,546	5,890
60 - 89 Days Past Due	171	238
Greater Than 90 Days Past Due	24	19
Total Past Due	1,741	6,147
Current	3,733,358	3,284,489
Loans Past Due 90 Days or More Still Accruing Interest	24	19
Hardware
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	29	167
60 - 89 Days Past Due	643	32
Greater Than 90 Days Past Due	0	0
Total Past Due	672	199
Current	1,125,277	1,107,422
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Venture capital/private equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	4	7
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	4	7
Current	1,953,111	1,749,896
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Life science
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	153	207
60 - 89 Days Past Due	249	117
Greater Than 90 Days Past Due	0	0
Total Past Due	402	324
Current	1,107,659	1,076,468
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Premium wine
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	2,400	0
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	2,400	0
Current	640,741	554,886
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	71	280
60 - 89 Days Past Due	97	0
Greater Than 90 Days Past Due	0	0
Total Past Due	168	280
Current	389,145	378,619
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Real estate secured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	0	0
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	0	0
Current	828,401	683,254
Loans Past Due 90 Days or More Still Accruing Interest	0	0
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 - 59 Days Past Due	0	111
60 - 89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	0	111
Current	93,072	143,867
Loans Past Due 90 Days or More Still Accruing Interest	$ 0	$ 0